Alkyl-alkoxysilacyclic compounds

ABSTRACT

A method and composition for producing a low k dielectric film via chemical vapor deposition is provided. In one aspect, the method comprises the steps of: providing a substrate within a reaction chamber; introducing into the reaction chamber gaseous reagents including at least one structure-forming precursor comprising a silacyclic compound, and a porogen; applying energy to the gaseous reagents in the reaction chamber to induce reaction of the gaseous reagents to deposit a preliminary film on the substrate, wherein the preliminary film contains the porogen, and the preliminary film is deposited; and removing from the preliminary film at least a portion of the porogen contained therein and provide the film with pores and a dielectric constant of 2.7 or less.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/732,250 filed Jun. 5, 2015 which, in turn, claims priority to and thebenefit of U.S. provisional patent application Ser. No. 62/012,724,filed Jun. 16, 2014, which is incorporated herein by reference in itsentirety.

BACKGROUND OF THE INVENTION

Described herein is a composition and method for the formation of adielectric film using alkyl-alkoxysilacyclic compounds as a structureformer precursor(s). More specifically, described herein is acomposition and method for formation of a porous low dielectric constant(“low k” film or film having a dielectric constant of about 2.7 or less)film wherein the method is used to deposit the film is a chemical vapordeposition (CVD) method. The dielectric films, produced by thecompositions and methods described herein, can be used, for example, asinsulating layers in electronic devices.

The electronics industry utilizes dielectric materials as insulatinglayers between circuits and components of integrated circuits (IC) andassociated electronic devices. Line dimensions are being reduced inorder to increase the speed and memory storage capability ofmicroelectronic devices (e.g., computer chips). As the line dimensionsdecrease, the insulating requirements for the interlayer dielectric(ILD) become much more rigorous. Shrinking the spacing requires a lowerdielectric constant to minimize the RC time constant, where R is theresistance of the conductive line and C is the capacitance of theinsulating dielectric interlayer. Capacitance (C) is inverselyproportional to spacing and proportional to the dielectric constant (k)of the interlayer dielectric (ILD). Conventional silica (SiO₂) CVDdielectric films produced from SiH₄ or TEOS (Si(OCH₂CH₃)₄,tetraethylorthosilicate) and O₂ have a dielectric constant k greaterthan 4.0. There are several ways in which industry has attempted toproduce silica-based CVD films with lower dielectric constants, the mostsuccessful being the doping of the insulating silicon oxide film withorganic groups providing dielectric constants ranging from about 2.7 toabout 3.5. This organosilica glass is typically deposited as a densefilm (density ˜1.5 g/cm³) from an organosilicon precursor, such as amethylsilane or siloxane, and an oxidant, such as O₂ or N₂O.Organosilica glass will be herein be referred to as OSG. As dielectricconstant or “k” values drop below 2.7 with higher device densities andsmaller dimensions, the industry has exhausted most of the suitable lowk compositions for dense films and has turned to various porousmaterials for improved insulating properties.

Patents, published applications, and publications in the field of porousILD by CVD methods field include: EP 1 119 035 A2 and U.S. Pat. No.6,171,945, which describe a process of depositing an OSG film fromorganosilicon precursors with labile groups in the presence of anoxidant such as N₂O and optionally a peroxide, with subsequent removalof the labile group with a thermal anneal to provide porous OSG; U.S.Pat. Nos. 6,054,206 and 6,238,751, which teach the removal ofessentially all organic groups from deposited OSG with an oxidizinganneal to obtain porous inorganic SiO₂; EP 1 037 275, which describesthe deposition of an hydrogenated silicon carbide film which istransformed into porous inorganic SiO₂ by a subsequent treatment with anoxidizing plasma; and U.S. Pat. No. 6,312,793 B1, WO 00/24050, and aliterature article Grill, A. Patel, V. Appl. Phys. Lett. (2001), 79(6),pp. 803-805, which all teach the co-deposition of a film from anorganosilicon precursor and an organic compound, and subsequent thermalanneal to provide a multiphase OSG/organic film in which a portion ofthe polymerized organic component is retained. In the latter references,the ultimate final composition of the films indicate residual porogenand a high hydrocarbon film content of approximately 80 to 90 atomic %.Further, the final films retain the SiO₂-like network, with substitutionof a portion of oxygen atoms for organic groups.

A challenge, which has been recognized in the industry, is that filmswith lower dielectric constants typically have higher porosity, whichleads to enhanced diffusion of species into the films, specifically gasphase diffusion. This increased diffusion can result in increasedremoval of carbon from the porous OSG film from processes such asetching of the film, plasma ashing of photoresist, and NH₃ plasmatreatment of copper surfaces. Carbon depletion in the OSG films cancause one or more of the following problems: an increase in thedielectric constant of the film; film etching and feature bowing duringwet cleaning steps; moisture absorption into the film due to loss ofhydrophobicity, pattern collapse of fine features during the wet cleansteps after pattern etch and/or integration issues when depositingsubsequent layers such as, without limitation, copper diffusionbarriers, for example Ta/TaN or advanced Co or MnN barrier layers.

Possible solutions to one or more of these problems are to use porousOSG films with increased carbon content. A first approach is to use aporogen which results in a higher retention of Si-Methyl (Me) groups inthe porous OSG layer. Unfortunately, as depicted in FIG. 1, therelationship between increasing Si-Me content typically leads todecreasing mechanical properties, thus the films with more Si-Me willnegatively impact mechanical strength which is important forintegration. A second approach has been to use a damage resistantporogen (DRP), such as, for example, the porogen disclosed in U.S. Pat.No. 8,753,985, which leaves additional amorphous carbon behind in thefilm after UV curing. In certain cases, this residual carbon does notnegatively impact the dielectric constant nor the mechanical strength.It is difficult, however, to get significantly higher carbon contents inthese films using the DRP.

Yet another solution proposed has been to use ethylene or methylenebridged disiloxanes of the general formulaR_(x)(RO)_(3-x)Si(CH₂)_(y)SiR_(z)(OR)_(3-z) where x=0-3, y=1 or 2,z=0-3. The use of bridged species is believed to avoid the negativeimpact to the mechanical by replacing bridging oxygen with a bridgingcarbon chain since the network connectivity will remain the same. Thisarises from the belief that replacing bridging oxygen with a terminalmethyl group will lower mechanical strength by lowering networkconnectivity. In this manner one, can replace an oxygen atom with 1-2carbon atoms to increase the atomic weight percent (%) C withoutlowering mechanical strength. These bridged precursors, however,generally have very high boiling points due to the increased molecularweight from having two silicon groups. The increased boiling point maynegatively impact the manufacturing process by making it difficult todeliver the chemical precursor into the reaction chamber as a gas phasereagent without condensing it in the vapor delivery line or process pumpexhaust.

Thus, there is a need in the art for a dielectric precursor thatprovides a film with increased carbon content upon deposition yet doesnot suffer the above-mentioned drawbacks.

BRIEF SUMMARY OF THE INVENTION

The method and composition described herein fulfill one or more needsdescribed above. The method and composition described herein use analkyl-alkoxysilacyclic compound(s) such as, for example,1-methyl-1-ethoxysilacyclopantane (MESCAP), as the structure formerwhich after co-deposition with a porogen precursor and, after UV curingto remove the porogen and harden the as-deposited film, provides aporous low k dielectric film that has similar mechanical properties asthe films that use a prior art structure former such asdiethoxymethylsilane (DEMS) at the same dielectric constant. Further,the films deposited using the alkyl-alkoxysilacyclic compounds describedherein as the structure former precursor(s) comprise a relatively higheramount of carbon. In addition, the alkyl-alkoxysilacyclic compound(s)described herein have a lower molecular weight (Mw) relative to otherprior art structure-former precursors such as bridged precursors, (e.g.,disilane or disiloxane precursors) which by nature of having 2 silicongroups have a higher Mw and higher boiling points, thereby making thealkyl-alkoxysilacyclic precursors described herein more convenient toprocess, for example, in a high volume manufacturing process.

Described herein is a porous dielectric film comprising: a materialrepresented by the formula Si_(v)O_(w)C_(x)H_(y)F_(z), wherev+w+x+y+z=100%, v is from 10 to 35 atomic %, w is from 10 to 65 atomic%, x is from 5 to 45 atomic %, y is from 10 to 50 atomic % and z is from0 to 15 atomic %, wherein the film has pores and a dielectric constantless than 2.7. In certain embodiments, the film comprises a highercarbon content (10-40%) as measured by X-ray photospectrometry (XPS) andexhibits a decreased depth of carbon removal when exposed to, forexample an O₂ or NH₃ plasma as measured by examining the carbon contentdetermined by XPS depth profiling.

In one aspect, there is provided a composition for a vapor deposition ofa dielectric film comprising a silacyclic compound having the followingFormula I:

wherein R¹ is independently selected from hydrogen, a linear or branchedC₁ to C₁₀ alkyl group, a linear or branched O₂ to C₁₀ alkenyl group, alinear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀ cyclic alkylgroup, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀ aryl group,and a C₃ to C₁₀ hetero-aryl group; R² is selected from hydrogen, alinear or branched C₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀alkenyl group, a linear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀cyclic alkyl group, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀aryl group, and a C₃ to C₁₀ hetero-aryl group; and R³ is selected from aC₃ to C₁₀ alkyl di-radical which forms a four-membered, five-membered,or six-membered cyclic ring with the Si atom and wherein the compound issubstantially free of one or more impurities selected from the groupconsisting of a halide and water.

In a further aspect, there is provided a chemical vapor depositionmethod for producing a porous dielectric film, comprising: providing asubstrate into a reaction chamber; introducing gaseous reagents into thereaction chamber wherein the gaseous reagents comprise: astructure-forming precursor comprising a silacyclic compound having thefollowing Formula I:

wherein R¹ is independently selected from hydrogen, a linear or branchedC₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀ alkenyl group, alinear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀ cyclic alkylgroup, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀ aryl group,and a C₃ to C₁₀ hetero-aryl group; R² is selected from hydrogen, alinear or branched C₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀alkenyl group, a linear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀cyclic alkyl group, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀aryl group, and a C₃ to C₁₀ hetero-aryl group; and R³ is selected from aC₃ to C₁₀ alkyl di-radical which forms a four-membered, five-membered,or six-membered cyclic ring with the Si atom, and a porogen; applyingenergy to the gaseous reagents in the reaction chamber to inducereaction of the gaseous reagents to deposit a preliminary film on thesubstrate, wherein the preliminary film contains the porogen; andremoving from the preliminary film substantially all of the porogen toprovide the porous film with pores and a dielectric constant less than2.7. In certain embodiments, the structure-forming precursor furthercomprises a hardening additive.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph showing the relationship between mechanical strength(Bulk Modulus GPa) and the Methyl (Me)/Si ratio in porous low kdielectric films obtained from computer modeling.

FIG. 2 is a graph that compares the carbon content vs. dielectricconstant for exemplary porous low k dielectric films using the methodand composition described herein comprising the structure former MESCAPand the porogen cyclooctane and prior art exemplary films comprising thestructure former DEMS and the porogen cyclooctane.

FIG. 3 demonstrates the increased resistance to carbon removal when thefilm is damaged using a NH₃ plasma.

DETAILED DESCRIPTION OF THE INVENTION

Described herein is a chemical vapor deposition (CVD) method forproducing the porous low k dielectric film, comprising: providing asubstrate within a reaction chamber; introducing into the reactionchamber gaseous reagents including at least one structure-formingprecursor comprising an alkyl-alkoxysilacyclic compound (also referredto herein as a silacyclic compound) such as, for example,1-methyl-1-ethoxy-1-silacyclopentane, and a porogen; applying energy tothe gaseous reagents in the reaction chamber to induce reaction of thegaseous reagents to deposit a preliminary film on the substrate, whereinthe preliminary film contains the porogen and the organosilicate glass;and removing from the preliminary film substantially all of the porogento provide the porous film with pores and a dielectric constant lessthan 2.7.

The alkyl-alkoxysilacyclic compounds described herein provide uniqueattributes that make it possible for one to incorporate more carboncontent in the dielectric film with minor impact on the mechanicalproperties of the dielectric film compared to prior art structure formerprecursors such as diethoxymethylsilane (DEMS). For example, DEMSprovides a mixed ligand system in DEMS with two alkoxy groups, onemethyl and one hydride which offers a balance of reactive sites andallows for the formation of more mechanically robust films whileretaining the desired dielectric constant desired. While not being boundby theory, the alkyl-alkoxysilacyclic precursors described herein suchas 1-methyl-1-ethoxy-1-silacyclopentane are assymetric in nature and mayoffer advantages over more symmetric precursors such as1,1-dimethyl-1-silacyclopentane or 1,1-diethoxy-1-silacyclopent-3-enewhich have been proposed. The incorporation of one alkyl and one alkoxygroup of the structure-forming precursor(s) described herein allows fora balance of mechanical strength and carbon incorporation at dielectricconstant of 2.7 or less.

The low k dielectric films are organosilica glass (“OSG”) films ormaterials. Organosilicates are candidates for low k materials, butwithout the addition of porogens to add porosity to these materials,their inherent dielectric constant is limited to as low as 2.7. Theaddition of porosity, where the void space has an inherent dielectricconstant of 1.0, reduces the overall dielectric constant of the film,generally at the cost of mechanical properties. Material propertiesdepend upon the chemical composition and structure of the film. Sincethe type of organosilicon precursor has a strong effect upon the filmstructure and composition, it is beneficial to use precursors thatprovide the required film properties to ensure that the addition of theneeded amount of porosity to reach the desired dielectric constant doesnot produce films that are mechanically unsound. The method andcomposition described herein provides the means to generate porous low kdielectric films that have a desirable balance of electrical andmechanical properties as well as other beneficial film properties ashigh carbon content to provide improved integration plasma resistance.

In certain embodiments of the method and composition described herein, alayer of silicon-containing dielectric material is deposited on at aleast a portion of a substrate via a chemical vapor deposition (CVD)process employing a reaction chamber. Suitable substrates include, butare not limited to, semiconductor materials such as gallium arsenide(“GaAs”), silicon, and compositions containing silicon such ascrystalline silicon, polysilicon, amorphous silicon, epitaxial silicon,silicon dioxide (“SiO₂”), silicon glass, silicon nitride, fused silica,glass, quartz, borosilicate glass, and combinations thereof. Othersuitable materials include chromium, molybdenum, and other metalscommonly employed in semiconductor, integrated circuits, flat paneldisplay, and flexible display applications. The substrate may haveadditional layers such as, for example, silicon, SiO₂, organosilicateglass (OSG), fluorinated silicate glass (FSG), boron carbonitride,silicon carbide, hydrogenated silicon carbide, silicon nitride,hydrogenated silicon nitride, silicon carbonitride, hydrogenated siliconcarbonitride, boronitride, organic-inorganic composite materials,photoresists, organic polymers, porous organic and inorganic materialsand composites, metal oxides such as aluminum oxide, and germaniumoxide. Still further layers can also be germanosilicates,aluminosilicates, copper and aluminum, and diffusion barrier materialssuch as, but not limited to, TiN, Ti(C)N, TaN, Ta(C)N, Ta, W, or WN.

In certain embodiments of the method and described herein, the layer ofsilicon-containing dielectric material is deposited on at least aportion of the substrate by introducing into the reaction chambergaseous reagents including at least one structure-forming precursorcomprising an alkyl-alkoxysilacyclic compound and a porogen precursor.

The method and composition described herein use a silacyclic compound asthe structure-forming precursor(s) according which have the followingstructure of Formula (I):

wherein R¹ is independently selected from hydrogen, a linear or branchedC₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀ alkenyl group, alinear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀ cyclic alkylgroup, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀ aryl group, aC₃ to C₁₀ hetero-aryl group; R² is selected from hydrogen, a linear orbranched C₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀ alkenylgroup, a linear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀ cyclicalkyl group, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀ arylgroup, a C₃ to C₁₀ hetero-aryl group; and R³ is selected from a C₃ toC₁₀ alkyl di-radical which forms a four-membered, five-membered, orsix-membered cyclic ring with the Si atom.

In the formula above and throughout the description, the term “alkyl”denotes a linear or branched functional group having from 1 to 10 carbonatoms. Exemplary linear alkyl groups include, but are not limited to,methyl, ethyl, n-propyl, butyl, pentyl, and hexyl groups. Exemplarybranched alkyl groups include, but are not limited to, iso-propyl,iso-butyl, sec-butyl, tert-butyl, iso-pentyl, tert-pentyl, iso-hexyl,and neo-hexyl. In certain embodiments, the alkyl group may have one ormore functional groups attached thereto such as, but not limited to, analkoxy group such as methoxy, ethoxy, iso-propoxy, and n-propoxy, adialkylamino group such as dimethylamino or combinations thereof,attached thereto. In other embodiments, the alkyl group does not haveone or more functional groups attached thereto. The alkyl group may besaturated or, alternatively, unsaturated.

In Formula I above and throughout the description, the term “cyclicalkyl” denotes a cyclic functional group having from 3 to 10 carbonatoms. Exemplary cyclic alkyl groups include, but are not limited to,cyclobutyl, cyclopentyl, cyclohexyl, and cyclooctyl groups.

In Formula I above and throughout the description, the term“hetero-cyclic” denotes a C₃ to C₁₀ hetero-cyclic alkyl group such as anepoxy group.

In Formula I above and throughout the description, the term “alkenylgroup” denotes a group which has one or more carbon-carbon double bondsand has from 2 to 10 or from 2 to 10 or from 2 to 6 carbon atoms.

In Formula I above and throughout the description, the term “alkynylgroup” denotes a group which has one or more carbon-carbon triple bondsand has from 3 to 10 or from 2 to 10 or from 2 to 6 carbon atoms.

In Formula I above and throughout the description, the term “aryl”denotes an aromatic cyclic functional group having from 5 to 10 carbonatoms, or from 6 to 10 carbon atoms. Exemplary aryl groups include, butare not limited to, phenyl, benzyl, chlorobenzyl, tolyl, and o-xylyl.

In Formula I above and throughout the description, the term“hetero-aryl” denotes a C₃ to C₁₀ hetero-cyclic aryl group1,2,3-triazolyl, pyrrolyl, and furanyl.

In Formula I above, substituent R³ is a C₃ to C₁₀ alkyl di-radical whichforms a four-membered, five-membered, or six-membered cyclic ring withthe Si atom. As the skilled person will understand, R³ is a substitutedor unsubstituted hydrocarbon chain which links with the Si atom togetherto form a ring in Formula I wherein the ring is a four-membered,five-membered, or six-membered ring. In these embodiments, the ringstructure can be unsaturated such as, for example, a cyclic alkyl ring,or saturated, for example, an aryl ring.

In certain embodiments of Formula I, R¹ is selected from the groupconsisting of hydrogen, methyl, and ethyl, R² is selected from the groupconsisting of methyl, ethyl, and isopropyl, and R³ forms afour-membered, five-membered, or six-membered cyclic ring with the Siatom. Examples of these embodiments are as follows:

In one particular embodiment, the composition and method describedherein uses the alkyl-alkoxysilacyclic compound,1-methyl-1-ethoxysilacyclopentane (MESCAP), as the structure-formingprecursor which has the following structure:

The silacyclic compounds described herein and methods and compositionscomprising same are preferably substantially free of one or moreimpurities such as without limitation, halide ions and water. As usedherein, the term “substantially free” as it relates to an impurity means100 parts per million (ppm) or less, 50 ppm or less, 10 ppm or less, and5 ppm or less of the impurity.

In one particular embodiment, the silacyclic compounds contain halideions (or halides) such as, for example, chlorides and fluorides,bromides, and iodides, means 100 parts per million (ppm) or less, 50 ppmor less, 10 ppm or less, and 5 ppm or less of the impurity or 0 ppm.Chlorides are known to act as decomposition catalysts foralkyl-alkoxysilacyclic compounds as well as potential contaminate todetrimental to performance of electronic device. The gradual degradationof the silacyclic compounds may directly impact the film depositionprocess making it difficult for the semiconductor manufacturer to meetfilm specifications. In addition, the shelf-life or stability isnegatively impacted by the higher degradation rate of the silacycliccompounds thereby making it difficult to guarantee a 1-2 yearshelf-life. Therefore, the accelerated decomposition of the silacycliccompounds presents safety and performance concerns related to theformation of these flammable and/or pyrophoric gaseous byproducts.

Compositions according to the present invention that are substantiallyfree of halides can be achieved by (1) reducing or eliminating chloridesources during chemical synthesis, and/or (2) implementing an effectivepurification process to remove chloride from the crude product such thatthe final purified product is substantially free of chlorides. Chloridesources may be reduced during synthesis by using reagents that do notcontain halides such as chlorodislanes, bromodisilanes, or iododislanesthereby avoiding the production of by-products that contain halide ions.In addition, the aforementioned reagents should be substantially free ofchloride impurities such that the resulting crude product issubstantially free of chloride impurities. In a similar manner, thesynthesis should not use halide based solvents, catalysts, or solventswhich contain unacceptably high levels of halide contamination. Thecrude product may also be treated by various purification methods torender the final product substantially free of halides such aschlorides. Such methods are well described in the prior art and, mayinclude, but are not limited to, purification processes such asdistillation, or adsorption. Distillation is commonly used to separateimpurities from the desire product by exploiting differences in boilingpoint. Adsorption may also be used to take advantage of the differentialadsorptive properties of the components to effect separation such thatthe final product is substantially free of halide. Adsorbents such as,for example, commercially available MgO—Al₂O₃ blends can be used toremove halides such as chloride.

Whereas prior art silicon-containing structure-forming precursors, forexample DEMS, polymerize, once energized in the reaction chamber, toform a structure having an —O— linkage (e.g., —Si—O—Si— or —Si—O—C—) inthe polymer backbone, it is believed that silacyclic compounds, such as,for example, the MESCAP molecule polymerizes to form a structure where,some of the —O— bridge in the backbone is replaced with a —CH₂—methylene or —CH₂CH₂— ethylene bridge(s). In films deposited using DEMSas the structure forming precursor where the carbon exists mainly in theform of terminal Si-Me groups there is a relationship between the %Si-Me (directly related to % C) versus mechanical strength, see forexample the modeling work shown in FIG. 1 where the replacement of abridging Si—O—Si group with two terminal Si-Me groups decreases themechanical properties because the network structure is disrupted. In thecase of the silacyclic compounds it is believed that the cyclicstructure is broken either during the film deposition or the cureprocess (to remove at least a portion of, or substantially all, of theporogen precursor contained in the as-deposited film) to form SiCH₂Si orSiCH₂CH₂Si bridging groups. In this manner, one can incorporate carbonin the form of a bridging group so that, from a mechanical strengthview, the network structure is not disrupted by increasing the carboncontent in the. Not being bound by theory, this attribute adds carbon tothe film, which allows the film to be more resilient to carbon depletionof the porous OSG film from processes such as etching of the film,plasma ashing of photoresist, and NH₃ plasma treatment of coppersurfaces. Carbon depletion in the OSG films can cause increases in thedefective dielectric constant of the film, problems with film etchingand feature bowing during wet cleaning steps, and/or integration issueswhen depositing copper diffusion barriers.

The composition for depositing the dielectric film described hereincomprises: from about 5 to about 60 weight percent of structure formingprecursor comprising the silacyclic compound(s) having Formula I; andfrom about 40 to about 95 weight percent or porogen precursor dependingon the nature of the porogen precursor.

In certain embodiments of the method and composition comprised herein,the structure forming precursor further comprises a hardening additivewhich will increase the mechanical strength, examples of hardeningadditives are tetraalkoxysilanes, such as for example, tetrethoxysilane(TEOS) or tetramethoxysilane (TMOS). In embodiments wherein a hardeningadditive is used, the composition of the structure former portioncomprises from about 30 to about 95 weight percent structure formingprecursor comprising the silacyclic compound(s) having Formula I; fromabout 5 to about 70 weight percent of hardening additive; and about 40to about 95 weight percent of the total precursor flow of porogenprecursor.

As previously mentioned, the gaseous reagents further comprises one ormore porogen precursors which is introduced into the reaction chamberalong with the at least one structure-forming precursor comprising asilacyclic compound such as, for example,1-methyl-1-ethoxysilacyclopentane. The following are non-limitingexamples of materials suitable for use as porogens for use according tothe present invention:

1) Cyclic hydrocarbons of the general formula C_(n)H₂n where n=4-14,where the number of carbons in the cyclic structure is between 4 and 10,and where there can be a plurality of simple or branched hydrocarbonssubstituted onto the cyclic structure.

-   -   Examples include: cyclohexane, 1,2,4-trimethylcyclohexane,        1-methyl-4-(1-methylethyl)cyclohexane, cyclooctane,        methylcyclooctane, methylcyclohexane, etc.

2) Linear or branched, saturated, singly or multiply unsaturatedhydrocarbons of the general formula C_(n)H_((2n+2)−2y) where n=2-20 andwhere y=0-n.

-   -   Examples include: ethylene, propylene, acetylene, neohexane,        1,3-butadiene, 2-methyl-1,3-butadiene,        2,3-dimethyl-2,3-butadiene, substituted dienes, etc.

3) Singly or multiply unsaturated cyclic hydrocarbons of the generalformula C_(n)H_(2n−2x) where x is the number of unsaturated sites in themolecule, n=4-14, where the number of carbons in the cyclic structure isbetween 4 and 10, and where there can be a plurality of simple orbranched hydrocarbons substituted onto the cyclic structure. Theunsaturation can be located inside endocyclic or on one of thehydrocarbon substituents to the cyclic structure.

-   -   Examples include, para-cymene, cyclooctene, 1,5-cyclooctadiene,        dimethyl-cyclooctadiene, cyclohexene, vinyl-cyclohexane,        dimethylcyclohexene, alpha-terpinene, pinene, limonene,        vinyl-cyclohexene, etc.

4) Bicyclic hydrocarbons of the general formula C_(n)H_(2n−2) wheren=4-14, where the number of carbons in the bicyclic structure is between4 and 12, and where there can be a plurality of simple or branchedhydrocarbons substituted onto the cyclic structure.

-   -   Examples include, norbornane, spiro-nonane,        decahydronaphthalene, etc.

5) Multiply unsaturated bicyclic hydrocarbons of the general formulaC_(n)H_(2n−(2+2x)) where x is the number of unsaturated sites in themolecule, n=4-14, where the number of carbons in the bicyclic structureis between 4 and 12, and where there can be a plurality of simple orbranched hydrocarbons substituted onto the cyclic structure. Theunsaturation can be located inside endocyclic or on one of thehydrocarbon substituents to the cyclic structure.

-   -   Examples include camphene, norbornene, norbornadiene,        5-Ethylidene-2-norbornene etc.

6) Tricyclic hydrocarbons of the general formula C_(n)H_(2n−4) wheren=4-14, where the number of carbons in the tricyclic structure isbetween 4 and 12, and where there can be a plurality of simple orbranched hydrocarbons substituted onto the cyclic structure.

Examples include adamantane.

Although the phrase “gaseous reagents” is sometimes used herein todescribe the reagents, the phrase is intended to encompass reagentsdelivered directly as a gas to the reactor, delivered as a vaporizedliquid, a sublimed solid and/or transported by an inert carrier gas intothe reactor.

In addition, the reagents can be carried into the reactor separatelyfrom distinct sources or as a mixture. The reagents can be delivered tothe reactor system by any number of means, preferably using apressurizable stainless steel vessel fitted with the proper valves andfittings to allow the delivery of liquid to the process reactor.

In addition to the structure forming species and the pore-formingspecies, additional materials can be introduced into the reactionchamber prior to, during and/or after the deposition reaction. Suchmaterials include, e.g., inert gas (e.g., He, Ar, N₂, Kr, Xe, etc.,which may be employed as a carrier gas for lesser volatile precursorsand/or which can promote the curing of the as-deposited materials andprovide a more stable final film) and reactive substances, such asoxygen-containing species such as, for example, O₂, O₃, and N₂O, gaseousor liquid organic substances, NH₃, H₂, CO₂, or CO. In one particularembodiment, the reaction mixture introduced into the reaction chambercomprises the at least one oxidant selected from the group consisting ofO₂, N₂O, NO, NO₂, CO₂, water, H₂O₂, ozone, and combinations thereof. Inan alternative embodiment, the reaction mixture does not comprise anoxidant.

Energy is applied to the gaseous reagents to induce the gases to reactand to form the film on the substrate. Such energy can be provided by,e.g., plasma, pulsed plasma, helicon plasma, high density plasma,inductively coupled plasma, remote plasma, hot filament, and thermal(i.e., non-filament) and methods. A secondary rf frequency source can beused to modify the plasma characteristics at the substrate surface.Preferably, the film is formed by plasma enhanced chemical vapordeposition (“PECVD”).

The flow rate for each of the gaseous reagents preferably ranges from 10to 5000 sccm, more preferably from 30 to 1000 sccm, per single 200 mmwafer. The individual rates are selected so as to provide the desiredamounts of structure-forming and porogen in the film. The actual flowrates needed may depend upon wafer size and chamber configuration, andare in no way limited to 200 mm wafers or single wafer chambers.

In certain embodiments, the film is deposited at a deposition rate ofabout 50 nanometers (nm) per minute.

The pressure in the reaction chamber during deposition ranges from about0.01 to about 600 torr or from about 1 to 15 torr.

The film is preferably deposited to a thickness of 0.002 to 10 microns,although the thickness can be varied as required. The blanket filmdeposited on a non-patterned surface has excellent uniformity, with avariation in thickness of less than 2% over 1 standard deviation acrossthe substrate with a reasonable edge exclusion, wherein e.g., a 5 mmoutermost edge of the substrate is not included in the statisticalcalculation of uniformity.

The porosity of the film can be increased with the bulk density beingcorrespondingly decreased to cause further reduction in the dielectricconstant of the material and extending the applicability of thismaterial to future generations (e.g., k<2.0).

As previously mentioned, at least a portion of the porogen precursor tosubstantially all of the porogen precursor contained in the as-depositedfilm is removed in a subsequent removal step. The removal of the porogenprecursor is performed by one or more of the following treatments: athermal treatment, an ultraviolet treatment, an electron beam treatment,a gamma radiation treatment, and combinations thereof. In one particularembodiment, the porogen removing step is conducted by a UV treatmentstep, a thermal treatment step, or a combination thereof. In the latterembodiment, the UV treatment step occurs during at least a portion ofthe thermal treatment.

The removal of at least a portion to substantially all of the porogencontained within the as-deposited film is assumed if there is nostatistically significant measured difference in atomic compositionbetween the annealed porous OSG and the analogous OSG without addedporogen. As used herein, the term “substantially free” as it relates toan removal of the porogen precursor in the as-deposited film means about2% or less, or about 1% or less, or about 50 ppm or less or about 10 ppmor less or about 5 ppm or less of the porogen as measured by XPS orother means. The inherent measurement error of the analysis method forcomposition (e.g., X-ray photoelectron spectroscopy (XPS), RutherfordBackscattering/Hydrogen Forward Scattering (RBS/HFS)) and processvariability both contribute to the range of the data. For XPS theinherent measurement error is Approx. +/−2 atomic %, while for RBS/HFSthis is expected to be larger, ranging from +/−2 to 5 atomic % dependingupon the species. The process variability will contribute a further +/−2atomic % to the final range of the data.

Preferred embodiments of the invention provide a thin film materialhaving a low dielectric constant and improved mechanical properties,thermal stability, and chemical resistance (to oxygen, aqueous oxidizingenvironments, etc.) relative to other porous low k dielectric filmsdeposited using other structure forming precursors known in the art. Thestructure forming precursors described herein comprising the silacycliccompound(s) having Formula I provides a higher incorporation into thefilm of carbon (preferably predominantly in the form of organic carbon,—CH_(x), where x is 1 to 3) whereby specific precursor ornetwork-forming chemicals are used to deposit films. In certainembodiments, the majority of the hydrogen in the film is bonded tocarbon.

The low k dielectric film deposited using the composition and methoddescribed herein comprise: (a) about 10 to about 35 atomic %, morepreferably about 20 to about 30 atomic % silicon; (b) about 10 to about65 atomic %, more preferably about 20 to about 45 atomic % oxygen; (c)about 10 to about 50 atomic %, more preferably about 15 to about 40atomic % hydrogen; (d) about 5 to about 40 atomic %, more preferablyabout 10 to about 45 atomic % carbon. Films may also contain about 0.1to about 15 atomic %, more preferably about 0.5 to about 7.0 atomic %fluorine, to improve one or more of materials properties. Lesserportions of other elements may also be present in certain films of theinvention. OSG materials are considered to be low k materials as theirdielectric constant is less than that of the standard materialtraditionally used in the industry—silica glass. The materials of theinvention can be provided by adding pore-forming species or porogens tothe deposition procedure, incorporating the porogens into theas-deposited (i.e., preliminary) OSG film and removing substantially allof the porogens from the preliminary film while substantially retainingthe terminal Si—CH₃ groups or bridging —(CH₂)_(x)— of the preliminaryfilm to provide the product film. The product film is porous OSG and hasa dielectric constant reduced from that of the preliminary film as wellas from an analogous film deposited without porogens. It is important todistinguish the film of the present invention as porous OSG, as opposedto a porous inorganic SiO₂, which lacks the hydrophobicity provided bythe organic groups in OSG.

Silica produced by CVD TEOS, for example, has an inherent free volumepore size determined by positron annihilation lifetime spectroscopy(PALS) analysis to be about 0.6 nm in equivalent spherical diameter. Thepore size of the inventive films as determined by small angle neutronscattering (SANS) or PALS is preferably less than 5 nm in equivalentspherical diameter, more preferably less than 2.5 nm in equivalentspherical diameter.

Total porosity of the film may be from 5 to 75% depending upon theprocess conditions and the desired final film properties. Films of theinvention preferably have a density of less than 2.0 g/ml, oralternatively, less than 1.5 g/ml or less than 1.25 g/ml. Preferably,films of the invention have a density at least 10% less than that of ananalogous OSG film produced without porogens, more preferably at least20% less.

The porosity of the film need not be homogeneous throughout the film. Incertain embodiments, there is a porosity gradient and/or layers ofvarying porosities. Such films can be provided by, e.g., adjusting theratio of porogen to precursor during deposition.

Films of the invention have a lower dielectric constant relative tocommon OSG materials. Preferably, films of the invention have adielectric constant at least 0.3 less than that of an analogous OSG filmproduced without porogens, more preferably at least 0.5 less. Preferablya Fourier transform infrared (FTIR) spectrum of a porous film of theinvention is substantially identical to a reference FTIR of a referencefilm prepared by a process substantially identical to the method exceptfor a lack of any porogen.

Films of the invention may also contain fluorine, in the form ofinorganic fluorine (e.g., Si—F). Fluorine, when present, is preferablycontained in an amount ranging from 0.5 to 7 atomic %.

Films of the invention are thermally stable, with good chemicalresistance. In particular, preferred films after anneal have an averageweight loss of less than 1.0 wt %/hr isothermal at 425° C. under N₂.Moreover, the films preferably have an average weight loss of less than1.0 wt %/hr isothermal at 425° C. under air.

The films are suitable for a variety of uses. The films are particularlysuitable for deposition on a semiconductor substrate, and areparticularly suitable for use as, e.g., an insulation layer, aninterlayer dielectric layer and/or an inter-metal dielectric layer. Thefilms can form a conformal coating. The mechanical properties exhibitedby these films make them particularly suitable for use in Al subtractivetechnology and Cu damascene or dual damascene technology.

The films are compatible with chemical mechanical planarization (CMP)and anisotropic etching, and are capable of adhering to a variety ofmaterials, such as silicon, SiO₂, Si₃N₄, OSG, FSG, silicon carbide,hydrogenated silicon carbide, silicon nitride, hydrogenated siliconnitride, silicon carbonitride, hydrogenated silicon carbonitride,boronitride, antireflective coatings, photoresists, organic polymers,porous organic and inorganic materials, metals such as copper andaluminum, and diffusion barrier layers such as but not limited to TiN,Ti(C)N TaN, Ta(C)N, Ta, W, WN or W(C)N. The films are preferably capableof adhering to at least one of the foregoing materials sufficiently topass a conventional pull test, such as ASTM D3359-95a tape pull test. Asample is considered to have passed the test if there is no discernibleremoval of film.

Thus in certain embodiments, the film is an insulation layer, aninterlayer dielectric layer, an inter-metal dielectric layer, a cappinglayer, a chemical-mechanical planarization (CMP) or etch stop layer, abarrier layer or an adhesion layer in an integrated circuit.

Although the films described herein are uniformly deposited dielectricfilms, the films as used in a full integration structure may actuallyconsist of several sandwiched layers with for example a thin layer atthe bottom or top which contains little or no porogen being deposited,or a layer may be deposited under conditions where there is a lowerporogen precursor flow ratio alternatively for example a layer may bedeposited at higher plasma power such that not all the porogen precursorcan be removed by UV treatment. These sandwich layers may be utilized toenhance secondary integration properties such as for example adhesion,etch selectivity or electromigration performance.

Although the invention is particularly suitable for providing films andproducts of the invention are largely described herein as films, theinvention is not limited thereto. Products of the invention can beprovided in any form capable of being deposited by CVD, such ascoatings, multilaminar assemblies, and other types of objects that arenot necessarily planar or thin, and a multitude of objects notnecessarily used in integrated circuits. Preferably, the substrate is asemiconductor.

In addition to the inventive OSG products, the present inventionincludes the process by which the products are made, methods of usingthe products and compounds and compositions useful for preparing theproducts. For example, a process for making an integrated circuit on asemiconductor device is disclosed in U.S. Pat. No. 6,583,049, which isherein incorporated by reference.

The porogen in the deposited film may or may not be in the same form asthe porogen introduced to the reaction chamber. As well, the porogenremoval process may liberate the porogen or fragments thereof from thefilm. In essence, the porogen reagent (or porogen substituent attachedto the precursor), the porogen in the preliminary film, and the porogenbeing removed may or may not be the same species, although it ispreferable that they all originate from the porogen reagent (or porogensubstituent). Regardless of whether or not the porogen is unchangedthroughout the inventive process, the term “porogen” as used herein isintended to encompass pore-forming reagents (or pore-formingsubstituents) and derivatives thereof, in whatever forms they are foundthroughout the entire process of the invention.

Compositions of the invention can further comprise, e.g., at least onepressurizable vessel (preferably of stainless steel) fitted with theproper valves and fittings to allow the delivery of porogen, and MESCAPprecursor to the process reactor. The contents of the vessel(s) can bepremixed. Alternatively, porogen and precursor can be maintained inseparate vessels or in a single vessel having separation means formaintaining the porogen and precursor separate during storage. Suchvessels can also have means for mixing the porogen and precursor whendesired.

The porogen is removed from the preliminary (or as-deposited) film by acuring step, which can comprise thermal annealing, chemical treatment,in-situ or remote plasma treating, photocuring (e.g., UV) and/ormicrowaving. Other in-situ or post-deposition treatments may be used toenhance materials properties like hardness, stability (to shrinkage, toair exposure, to etching, to wet etching, etc.), integrity, uniformityand adhesion. Such treatments can be applied to the film prior to,during and/or after porogen removal using the same or different meansused for porogen removal. Thus, the term “post-treating” as used hereindenotes treating the film with energy (e.g., thermal, plasma, photon,electron, microwave, etc.) or chemicals to remove porogens and,optionally, to enhance materials properties.

The conditions under which post-treating are conducted can vary greatly.For example, post-treating can be conducted under high pressure or undera vacuum ambient.

UV annealing is a preferred method conducted under the followingconditions.

The environment can be inert (e.g., nitrogen, CO₂, noble gases (He, Ar,Ne, Kr, Xe), etc.), oxidizing (e.g., oxygen, air, dilute oxygenenvironments, enriched oxygen environments, ozone, nitrous oxide, etc.)or reducing (dilute or concentrated hydrogen, hydrocarbons (saturated,unsaturated, linear or branched, aromatics), etc.). The pressure ispreferably about 1 Torr to about 1000 Torr, more preferably atmosphericpressure. However, a vacuum ambient is also possible for thermalannealing as well as any other post-treating means. The temperature ispreferably 200-500° C., and the temperature ramp rate is from 0.1 to 100deg ° C./min. The total UV annealing time is preferably from 0.01 min to12 hours.

Chemical treatment of the OSG film is conducted under the followingconditions.

The use of fluorinating (HF, SIF₄, NF₃, F₂, COF₂, CO₂F₂, etc.),oxidizing (H₂O₂, O₃, etc.), chemical drying, methylating, or otherchemical treatments that enhance the properties of the final material.Chemicals used in such treatments can be in solid, liquid, gaseousand/or supercritical fluid states.

Supercritical fluid post-treatment for selective removal of porogensfrom an organosilicate film is conducted under the following conditions.

The fluid can be carbon dioxide, water, nitrous oxide, ethylene, SF₆,and/or other types of chemicals. Other chemicals can be added to thesupercritical fluid to enhance the process. The chemicals can be inert(e.g., nitrogen, CO₂, noble gases (He, Ar, Ne, Kr, Xe), etc.), oxidizing(e.g., oxygen, ozone, nitrous oxide, etc.), or reducing (e.g., dilute orconcentrated hydrocarbons, hydrogen, etc.). The temperature ispreferably ambient to 500° C. The chemicals can also include largerchemical species such as surfactants. The total exposure time ispreferably from 0.01 min to 12 hours.

Plasma treating for selective removal of labile groups and possiblechemical modification of the OSG film is conducted under the followingconditions.

The environment can be inert (nitrogen, CO₂, noble gases (He, Ar, Ne,Kr, Xe), etc.), oxidizing (e.g., oxygen, air, dilute oxygenenvironments, enriched oxygen environments, ozone, nitrous oxide, etc.),or reducing (e.g., dilute or concentrated hydrogen, hydrocarbons(saturated, unsaturated, linear or branched, aromatics), etc.). Theplasma power is preferably 0-5000 W. The temperature is preferablyambient to 500° C. The pressure is preferably 10 mtorr to atmosphericpressure. The total curing time is preferably 0.01 min to 12 hours.

UV curing for selective removal of porogens from an organosilicate filmis conducted under the following conditions.

The environment can be inert (e.g., nitrogen, CO₂, noble gases (He, Ar,Ne, Kr, Xe), etc.), oxidizing (e.g., oxygen, air, dilute oxygenenvironments, enriched oxygen environments, ozone, nitrous oxide, etc.),or reducing (e.g., dilute or concentrated hydrocarbons, hydrogen, etc.).The temperature is preferably ambient to 500° C. The power is preferably0 to 5000 W. The wavelength is preferably IR, visible, UV or deep UV(wavelengths<200 nm). The total UV curing time is preferably 0.01 min to12 hours.

Microwave post-treatment for selective removal of porogens from anorganosilicate film is conducted under the following conditions.

The environment can be inert (e.g., nitrogen, CO₂, noble gases (He, Ar,Ne, Kr, Xe), etc.), oxidizing (e.g., oxygen, air, dilute oxygenenvironments, enriched oxygen environments, ozone, nitrous oxide, etc.),or reducing (e.g., dilute or concentrated hydrocarbons, hydrogen, etc.).The temperature is preferably ambient to 500° C. The power andwavelengths are varied and tunable to specific bonds. The total curingtime is preferably from 0.01 min to 12 hours.

Electron beam post-treatment for selective removal of porogens orspecific chemical species from an organosilicate film and/or improvementof film properties is conducted under the following conditions.

The environment can be vacuum, inert (e.g., nitrogen, CO₂, noble gases(He, Ar, Ne, Kr, Xe), etc.), oxidizing (e.g., oxygen, air, dilute oxygenenvironments, enriched oxygen environments, ozone, nitrous oxide, etc.),or reducing (e.g., dilute or concentrated hydrocarbons, hydrogen, etc.).The temperature is preferably ambient to 500° C. The electron densityand energy can be varied and tunable to specific bonds. The total curingtime is preferably from 0.001 min to 12 hours, and may be continuous orpulsed. Additional guidance regarding the general use of electron beamsis available in publications such as: S. Chattopadhyay et al., Journalof Materials Science, 36 (2001) 4323-4330; G. Kloster et al.,Proceedings of IITC, Jun. 3-5, 2002, SF, CA; and U.S. Pat. Nos.6,207,555 B1, 6,204,201 B1 and 6,132,814 A1. The use of electron beamtreatment may provide for porogen removal and enhancement of filmmechanical properties through bond-formation processes in matrix.

The invention will be illustrated in more detail with reference to thefollowing Examples, but it should be understood that the it is notdeemed to be limited thereto.

EXAMPLES

Exemplary films or 200 mm wafer processing were formed via a plasmaenhanced CVD (PECVD) process using an Applied Materials Precision-5000system in a 200 mm D×Z reaction chamber or vacuum chamber that wasfitted with an Advance Energy 200 RF generator from a variety ofdifferent chemical precursors and process conditions. The PECVD processgenerally involved the following basic steps: initial set-up andstabilization of gas flows, deposition of the film onto the siliconwafer substrate, and purge/evacuation of chamber prior to substrateremoval. After the deposition, the films were subjected to UV annealing.UV annealing was performed using a Fusion UV system with a broad band UVbulb, with the wafer held under a helium gas flow at one or morepressures below <10 torr and at one or more temperatures <400° C. Theexperiments were conducted on p-type Si wafers (resistivity range=8-12Ohm-cm).

Thickness and refractive index were measured on an SCI FilmTek 2000Reflectometer. Dielectric constants were determined using Hg probetechnique on mid-resistivity p-type wafers (range 8-12 ohm-cm). FTIRspectra were measured using a Nicholet Nexxus 470 spectrometer. InComparative Example 1 and Example 1 and mechanical properties weredetermined using MTS Nano Indenter. Compositional data were obtained byx-ray photoelectron spectroscopy (XPS) on a Physical Electronics 5000LSand are provided in atomic weight percent. The atomic weight percent %values reported in the tables do not include hydrogen.

Comparative Example 1: Deposition of Porous OSG Films fromDiethyoxymethylsilane (DEMS) and Cyclooctane

A composite layer of the structure former DEMS and porogen precursorcyclooctane was deposited using the following process conditions for 200mm processing. The precursors were delivered to the reaction chamber viadirect liquid injection (DLI) at a flow rate of 960 milligrams/minute(mg/min) cyclooctane and 240 mg/min using 200 standard cubic centimeters(sccm) CO₂ carrier gas flow, 10 sccm O₂, 350 milli-inch showerhead/waferspacing, 275° C. wafer chuck temperature, 8 Torr chamber pressure towhich a 600 W plasma was applied. The resulting film was then UVannealed to remove the cyclooctane porogen and mechanically enhance thefilm. Various attributes of the film (e.g., dielectric constant (k),modulus (GPa) and atomic weight percent carbon (% C)) were obtained asdescribed above and are provided in Table 1.

Comparative Example 2: Deposition of Porous OSG Films from1,1-Diethoxy-1-silacyclobutane (DESCB) and Cyclooctane

A composite layer of the structure former DEMS and porogen precursorcyclooctane was deposited using the following process conditions for 200mm processing. The precursors were delivered to the reaction chamber viadirect liquid injection (DLI) at a flow rate of 1120 milligrams/minute(mg/min) cyclooctane and 280 mg/min using 200 standard cubic centimeters(sccm) CO₂ carrier gas flow, 20 sccm O2, 350 milli-inch showerhead/waferspacing, 250° C. wafer chuck temperature, 8 Torr chamber pressure towhich a 700 W plasma was applied. The resulting film was then UVannealed to remove the cyclooctane porogen and mechanically enhance thefilm. Various attributes of the film (e.g., dielectric constant (k),modulus (GPa) and atomic weight percent carbon (% C)) were obtained asdescribed above and are provided in Table 1.

Example 1: Deposition of Porous OSG Film from1-Methyl-1-Ethoxy-1-silacyclopentane (MESCAP) and Cyclooctane

A composite layer of structure former MESCAP and porogen precursorcyclooctane was deposited using the following process conditions for 200mm processing. The precursors were delivered to the reaction chamber viadirect liquid injection (DLI) at flow rate of 960 mg/min cyclooctane and240 mgm of MESCAP were delivered to the chamber via DLI using 200 sccmCO₂ carrier gas flow, 20 sccm O2, 350 milli-inch showerhead/waferspacing, 250° C. wafer chuck temperature, 8 Torr chamber pressure towhich a 600 W plasma was applied. The resulting film was then UVannealed to remove the porogen and mechanically enhance the film.Various attributes of the film (e.g., dielectric constant (k), modulus(GPa) and atomic weight percent carbon (% C)) were obtained as describedabove and are provided in Table 1.

Example 2: Deposition of Porous OSG Film from1-Methyl-1-isopropoxy-1-silacyclopentane (MPSCAP) and Cyclooctane

A composite layer of structure former MPSCAP and porogen precursorcyclooctane was deposited using the following process conditions for 200mm processing. The precursors were delivered to the reaction chamber viadirect liquid injection (DLI) at flow rate of 840 mg/min cyclooctane and360 mgm of MPSCAP were delivered to the chamber via DLI using 200 sccmCO₂ carrier gas flow, 20 sccm O2, 350 milli-inch showerhead/waferspacing, 250° C. wafer chuck temperature, 8 Torr chamber pressure towhich a 700 W plasma was applied. The resulting film was then UVannealed to remove the porogen and mechanically enhance the film.Various attributes of the film (e.g., dielectric constant (k), modulus(GPa) and atomic weight percent carbon (% C)) were obtained as describedabove and are provided in Table 1.

TABLE 1 Comparative Film Properties for films deposited using DEMS,MESCAP, MPSCAP, or DESCB with cyclooctane as the porogen precursor. Filmk Modulus (Gpa) % C (XPS) DEMS/Cyclooctane 2.32 7.57 13.2%MESCAP/Cyclooctane 2.36 6.90 22.6% MPSCAP/Cyclooctane 2.4 6.30   27%DESCB/cyclooctane 2.33 5.15 23.4%

TABLE 2 Film Properties for MESCAP/Cyclooctane Deposited Under VariousConditions with Chamber Pressure of 8 torr and Temperature of 250° C.MESCAP Cyclooctane O₂ Power Flow Flow Flow Modulus Hardness (watts)(mg/min) (mg/min) (sccm) Dielectric (GPa) (GPa) % C % O % Si 600 200 80010 2.4 7.15 1.28 31 37.2 31.6 600 240 960 10 2.44 8.67 1.51 25.4 42.632.2 600 300 700 10 2.45 8.39 1.54 30.9 37.7 31.4 600 360 840 10 2.4910.48 1.9 27 41.7 31.1 600 330 770 15 2.39 8.31 1.58 24.6 42.7 32.2 600330 770 20 2.36 7.96 1.53 22.6 44.4 33

Tables 1 and 2 show that films made using MESCAP, and the isopropoxyderivative MPSCAP, as the structure former and the cyclooctane porogenprecursor have an increased amount of carbon and similar modulusrelative to films made using the DEMS structure-forming precursor andthe same porogen. Table 1 also includes data for Comparative Example 2wherein 1,1-diethoxy-1-silacyclobutane, a symmetric silacyclic compoundwas used as the structure former precursor and had a higher % C than theDEMS-deposited films but lower mechanical properties.

Example 3: Depositions for Dielectric Films Using DEMS, MESCAP, andMESCAP and a Hardening Additive (HA) as the Structure Former andCyclooctane as the Porogen Precursor

Certain experiments used three hundred (300) mm wafer processing whichwere conducted on an Applied Materials Producer® SE. Like the 200 mmprocessing described above, the PECVD process generally involved thefollowing basic steps: initial set-up and stabilization of gas flows,deposition of the film onto the silicon wafer substrate, andpurge/evacuation of chamber prior to substrate removal. The 300 mmdepositions were conducted on a Producer® SE Twin low k chamberconfigured with a TEOS faceplate (AMAT part number: 0040-95475). Thechamber is fitted with an Advanced Energy APEX 3013 RF generator (twoper twin chamber). Helium was used as the carrier gas for alldepositions on the Producer. As-deposited films from the Producer® SElow k chamber were UV-cured on the Producer® SE NanoCure™ UV chamberunder an argon gas flow at one or more pressures <10 Torr pressure andat one or more pedestal set point temperatures ≤400° C. The experimentswere conducted on p-type Si wafers (resistivity range=8-12 Ohm-cm).

Thickness and refractive index were measured on an SCI FilmTek 2000Reflectometer. For Examples 3 and the 300 mm films, mechanicalproperties of the films were measured by nanoindentation using anAgilent G200 Nanoindenter. Indentations are performed to a maximumpenetration depth of 50% film thickness with a DCM indenter head usingthe continuous stiffness measurement (CSM) option. Modulus and hardnessmeasurements are reported at 10% of the film thickness. Further, themodulus measurements are compensated for the elastic influence of thesilicon substrate. Because of this compensation for substrate influence,the reported moduli are roughly 25% less than the values which would bedetermined by the Oliver-Pharr analysis alone. FTIR spectra for 300 mmwafers were collected using a Thermo Fisher Scientific Model iS 50spectrometer fitted with a Pike Technologies Map300 for handling 12 inchwafers. FTIR spectra for 200 mm wafers were measured using a NicoletNexxus 470 spectrometer. Dielectric constants were performed using aMaterials Development Corporation (MDC) mercury probe calibrated withthermal oxides standards.

Atomic composition was determined using X-Ray photospectrometry (XPS) ona PHI 5000VersaProbe Spectrometer equipped with Multiple Channel Plates(MCD) and a focused Al monochromatic X-ray source. Bulk composition isexamined over a 200 μm area after removal of ˜2000 Å by Ar⁺ sputtering.The atomic % values reported in the tables do not include hydrogen.

A series of depositions of porous low k dielectric films were depositedusing either DEMS or MESCAP as the structure former and cyclooctane asthe porogen precursor on a 200 mm PECVD reactor under a variety ofprocess conditions range from 500-700 W plasma power, 5-9 torr chamberpressure, 0.30-0.60 inch electrode spacing, 200-300 C substratetemperature, 10-50 sccm O2 flow, 200-400 sccm CO₂ or He carrier gasflow, 0.9-1.5 gram/minute total liquid flow of a 30:70-10:90 ratio ofOSG precursor to Cyclooctane porogen precursor. The carbon content wasmeasured by XPS as described herein. FIG. 2 shows the relationshipbetween the carbon content (%) of porous low k DEMS/cyclooctane andMESCAP/cyclooctane films having different dielectric constants. As FIG.2 shows, the prior art or DEMS/cyclooctane porous low k films had anarrow range of carbon content or from about 10 to about 20 atomic % asthe dielectric constant increased from about ˜2.3 to about ˜2.8. Bycontrast, the MESCAP/cyclooctane films described herein had a widerrange of carbon content or from about 9 to about 50 atomic % over thesame dielectric constant range. This illustrates one of the importantadvantages of using the alkyl-alkoxysilacyclic compounds describedherein such as MESCAP versus other prior art structure formers fordepositing a porous low K dielectric film which is for similar values ofthe dielectric constant, the alkyl-alkoxysilacyclic precursor MESCAPpermits a much wider and tunable range of carbon content.

Table 3 provides a comparison of porous low k films with a dielectricconstant of k=2.4 using either DEMS, MESCAP, or a composition comprisingMESCAP and a hardening additive (HA) which was tetraethyl orthosilicateas the structure former and cyclooctane as the porogen precursor.Processing conditions for a given film were adjusted to obtain a highelastic modulus, high carbon content, or both and are provided in Table3. All films were processed using standard UV cure times as determinedby the time it takes to reach maximum mechanical strength withoutnegatively impacting the dielectric constant. Compared to theDEMS/Cyclooctane film, the two MESCAP/Cyclooctane films contained asignificantly greater carbon content, while maintaining a similarelastic modulus. Further, the MESCAP/Cyclooctane films in Table 3 showthat for a given dielectric constant, the ability to deposit highelastic modulus films with a tunable carbon content that greatly exceedsthat of prior art structure formers such as DEMS. In addition, for agiven class of films (e.g., MESCAP/cyclooctane), the elastic modulusdecreases as the carbon content increases.

TABLE 3 k = 2.4 Porous low-k films. DEMS/ MESCAP/ MESCAP/ MESCAP/HA/MESCAP/HA/ Cyclooctane Cyclooctane Cyclooctane Cyclooctane CyclooctanePower (W) 700 900 600 600 631 Temperature (° C.) 285 280 280 280 280Pressure (Torr) 8.0 8.0 8.0 7.5 7.5 Porogen Flow (mg/min) 3150 4375 30623062 3850 Structure Former Flow 350 625 438 438 550 (mg/min) O2 Flow(sccm) 87.5 50 50 100 100 Relative UV Cure Time 1.1X 1.0 1.0 1.0 1.0Dielectric Constant 2.4 2.4 2.4 2.4 2.4 Elastic Modulus (Gpa) 7.1 6.57.4 8 9.2 % Carbon 12 26 15 13 11 % Oxygen 54 42 50 53 55 % Silicon 3433 35 34 34

Table 3 also provides two porous low k films that used a mixture ofMESCAP and a hardening additive (HA) tetraethyl orthosilicate as thestructure former and cyclooctane as the porogen precursor. In theseexamples, the structure former was a 50:50 mixture of MESCAP andhardening additive by weight. Referring to the data in Table 3, the HAdecreased the carbon content of the film but increased the elasticmodulus of the film. Relative to the comparative DEMS/cyclooctane film,the k=2.4 MESCAP/HA/cyclooctane film with an elastic modulus of 8.0 GPahad a higher elastic modulus (a 13% increase) and a greater carboncontent (a 8% increase). The other k=2.4, MESCAP/HardeningAdditive/cyclooctane film in Table 3 exhibits an elastic modulus of 9.2GPa and a carbon content of 11%. The later film containing the HA in thestructure former had a significant increase in the elastic modulus (a30% increase), but a decrease in the carbon content (a 8% decrease)relative to the comparative DEMS/cyclooctane film. The examples in Table3 illustrate that the inherently higher carbon content of MESCAPprovides a clear advantage as a structure former since a hardeningadditive can be introduced into the structure former composition withouta detrimental loss in carbon content.

Table 4 provides a comparison of porous low k films with a dielectricconstant of k=2.3 using either DEMS, MESCAP, or a composition comprisingMESCAP and a HA or tetraethyl orthosilicate as the structure former andcyclooctane as the porogen precursor. Processing conditions for a givenfilm were adjusted to obtain a high elastic modulus, high carboncontent, or both and are provided in Table 4. The first column in Table4 shows a MESCAP/cyclooctane deposited film with an elastic modulus of5.7 GPa and a carbon content of 24 atomic percent. The second column inTable 4 shows a MESCAP/cyclooctance deposited film with an elasticmodulus of 6.0 GPa and a carbon content of 17%. These films illustratethat the carbon content of the films using MESCAP as the structureformer can be adjusted from 17 to 25 atomic percent with almost noimpact on the elastic modulus. The third entry in Table 4 shows aMESCAP/HA/cyclooctane deposited film with an elastic modulus of 7.9 GPaand a carbon content of 14%. The later exemplary films shows that theuse of the alkyl-alkoxysilacyclic precursor MESCAP provides or maintainsthe relatively higher carbon content in the film while maintainingmechanical properties because a HA can be introduced into thecomposition without a detrimental loss in carbon content.

TABLE 4 k = 2.3 Porous low-k films. MESCAP/ MESCAP/ MESCAP/HA/Cyclooctane Cyclooctane Cyclooctane Power (W) 803 600 695 Temperature (°C.) 280 280 280 Pressure (Torr) 8.0 8.0 7.5 Porogen Flow (mg/min) 35003150 4025 Structure Former Flow 500 350 575 (mg/min) O2 Flow (sccm) 5050 140 Relative UV Cure Time 1.0 1.0 1.0 Dielectric Constant 2.3 2.3 2.3Elastic Modulus (Gpa) 5.7 6 7.9 % Carbon 24 17 14 % Oxygen 33 48 33 %Silicon 43 35 53

Table 5 provides a further example of the inherent advantage of thealkyl-alkoxysilacyclic precursor MESCAP for deposited porous low k filmshaving a dielectric constant of 2.6. The first column in Table 5 shows aDEMS/cyclooctane film with a high elastic modulus of 11 GPa and a carboncontent of 11%. By contrast, the MESCAP/cyclooctane film had anequivalent elastic modulus (11 GPa), but an higher carbon content of 15atomic percent (a 36 percent increase relative to the comparative DEMSbased film).

TABLE 5 k = 2.6 Porous low-k films. DEMS/ MESCAP/ CyclooctaneCyclooctane Power (W) 700 600 Temperature (° C.) 285 285 Pressure (Torr)8.0 8.0 Porogen Flow (mg/min) 4050 4375 Structure Former Flow (mg/min)450 625 O2 Flow (sccm) 87.5 50 Relative UV Cure Time 1.1 1.0 DielectricConstant 2.6 2.6 Elastic Modulus (Gpa) 11 11 % Carbon 11 15 % Oxygen 5351 % Silicon 36 34

FIG. 3 shows with a dielectric constant of about 2.3 were deposited asin Example 1 using MESCAP (▴) or Comparative Example 1 using DEMS (●) asthe structure-forming precursor and cyclooctane as the porogenprecursor. Both films were exposed to a 15 second NH₃ plasma at 100 Wplasma power to model the plasma damage conditions seen in integration.The depth of the damage is indicated by the depth to which the carbonwas removed from the film as detected by XPS depth profiling sputtering.FIG. 3 shows that a higher carbon content was retained for the filmsdeposited using MESCAP as the structure-forming precursor compared tofilms deposited using DEMS as the structure-forming precursor and thatthe depth of damage as indicated by the depth to which the carbon wasremoved from the film is less for the films deposited using MESCAP.

Although illustrated and described above with reference to certainspecific embodiments and examples, the present invention is neverthelessnot intended to be limited to the details shown. Rather, variousmodifications may be made in the details within the scope and range ofequivalents of the claims and without departing from the spirit of theinvention. It is expressly intended, for example, that all rangesbroadly recited in this document include within their scope all narrowerranges which fall within the broader ranges.

The invention claimed is:
 1. A composition for a vapor deposition of adielectric film comprising a silacyclic compound having the followingFormula I:

wherein R¹ is independently selected from hydrogen, a linear or branchedC₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀ alkenyl group, alinear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀ cyclic alkylgroup, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀ aryl group,and a C₃ to C₁₀ hetero-aryl group; R² is selected from hydrogen, alinear or branched C₁ to C₁₀ alkyl group, a linear or branched C₂ to C₁₀alkenyl group, a linear or branched C₂ to C₁₀ alkynyl group, a C₃ to C₁₀cyclic alkyl group, a C₃ to C₁₀ hetero-cyclic alkyl group, a C₅ to C₁₀aryl group, and a C₃ to C₁₀ hetero-aryl group; and R³ is selected from aC₃ to C₁₀ alkyl di-radical which forms a four-membered, five-membered,or six-membered cyclic ring with the Si atom, wherein the compound issubstantially free of at least one impurity selected from the groupconsisting of halides and water.
 2. The composition of claim 1 whereinthe silacyclic compound comprises at least one selected from the groupconsisting of 1-methyl-1-methoxy-1-silacyclopentane,1-methyl-1-ethoxy-1-silacyclopentane,1-methyl-1-isopropoxy-1-silacyclopentane,1-methyl-1-propoxy-1-silacyclopentane, 1-methoxy-1-silacyclopentane,1-ethoxy-1-silacyclopentane, 1-methyl-1-methoxy-1-silacyclobutane,1-methyl-1-ethoxy-1-silacyclobutane, 1-methoxy-1-silacyclobutane,1-ethoxy-1-silacyclobutane, 1-methyl-1-methoxy-1-silacyclohexane,1-methyl-1-ethoxy-1-silacyclohexane,1-methyl-1-methoxy-1-silacyclohexane,1-methyl-1-ethoxy-1-silacyclohexane,1-methyl-1-isopropoxy-1-silacyclopentane,1-methyl-1-isopropoxy-1-silacyclobutane,1-methyl-1-isopropoxy-1-silacyclohexane,1-isopropoxy-1-silacyclopentane, 1-isopropoxy-1-silacyclobutane,1-isopropoxy-1-silacyclohexane and combinations thereof.
 3. Thecomposition of claim 1, wherein the halides comprise chloride ions. 4.The composition of claim 3, wherein the chloride ions, if present, arepresent at a concentration of 50 ppm or less.
 5. The composition ofclaim 3, wherein the composition has 0 ppm of chloride ion.
 6. Thecomposition of claim 4, wherein the chloride ions, if present, arepresent at a concentration of 10 ppm or less.
 7. The composition ofclaim 6, wherein the chloride ions, if present, are present at aconcentration of 5 ppm or less.
 8. The composition of claim 2 whereinthe silacyclic compound comprises1-methyl-1-isopropoxy-1-silacyclopentane.
 9. The composition of claim 2wherein the silacyclic compound comprises1-methyl-1-ethoxy-1-silacyclopentane.
 10. The composition of claim 8,wherein the halides comprise chloride ions.
 11. The composition of claim10, wherein the chloride ions, if present, are present at aconcentration of 50 ppm or less.
 12. The composition of claim 11,wherein the chloride ions, if present, are present at a concentration of10 ppm or less.
 13. The composition of claim 12, wherein the chlorideions, if present, are present at a concentration of 5 ppm or less. 14.The composition of claim 13, wherein the composition has 0 ppm ofchloride ion.